1. Field of the Invention
This invention relates in general to a motor speed control apparatus and method for a hard disk drive, and more particularly, to a motor speed control apparatus and method that can identify the type of rotor assembly installed in a hard disk drive.
2. Description of Related Art
A hard disk drive (HDD) has a magnetic disk contained in an enclosure, and said magnetic disk is rotationally driven by a spindle motor. In the enclosure, the positioning of a magnetic head is controlled on the disk by an actuator, and read/write operations for magnetic information are performed.
Here, the spindle motor performs feedback control of the speed. To be more specific, as shown in FIG. 4, the period of the spindle motor 102 is calculated as pulses by the MPU 103, the period, T.sub.n, is compared to a target value, T.sub.arget, a proportional operation and an integral operation are performed for difference E.sub.n, predetermined output value U.sub.n is converted by digital/analog conversion (DAC), pulse width modulation (PWM) and the like on the basis of feedback coefficients K.sub.1 associated with the proportional operation and K.sub.2 associated with the integral operation, and U.sub.n is output to a driver 106 that supplies an electric current to the spindle motor 102. In addition, the code 108 in FIG. 4 is a period preceding the current period and the following relationships can be obtained: EQU E.sub.n =T.sub.n -T.sub.arget EQU I.sub.n+1 =I.sub.n +E.sub.n EQU U.sub.n =K.sub.1 E.sub.n +K.sub.2 I.sub.n.
One or two magnetic disks 110 are selectively installed on the hub of the spindle motor 102, incidentally, and the hard disk drive system is provided as a single disk model or a dual disk model according to the number of magnetic disks 110.
Because a single disk and dual disks are different in terms of the moment of inertia, feedback coefficients suitable to a single disk are different from feedback coefficients suitable to dual disks.
For this reason, in the conventional means, a dummy disk is added to the actual magnetic disk to make the moment of inertia of the single disk model the same as the moment of inertia of the dual disk model so that common feedback coefficients can be used. Otherwise, another conventional means is used in which the medium value between the feedback coefficient is suitable to the single magnetic disk and another feedback coefficient suitable to the dual magnetic disks.
The hard disk drive, however, on the one hand, is not only required to have a high rotation accuracy but also, especially in the case of a small hard disk drive such as that used under conditions of frequent ON/OFF operation of a computer, to have a shorter startup time at the time of startup, and, in addition, it is desirable that these requirements be met under the conditions of low power consumption and downsizing. Adding a dummy disk is not preferable from the points of ensuring low power consumption and downsizing.
On the other hand, it is possible to prepare two electronic boards, one incorporating a control circuit for the motor speed control using feedback coefficients suitable to the single disk and the other incorporating a control circuit for the motor speed control using other feedback coefficients suitable to the dual disks, and to connect each of the electronic boards differing from each other for the single disk model and the dual disk model. However, preparing two different electronic boards causes a cost increase and board installation is also troublesome.
It can be seen then that there is a need for a motor speed control apparatus and a motor speed control method in a motor having selectively installed rotor assemblies with different moments of inertia that can identify the type of rotor assembly installed to the motor.
It can also be seen that there is a need for determining feedback coefficients suitable to the identified rotor assembly in an automatic manner at the time the motor is started up, and performing speed control using said feedback coefficients suitable to the motor, wherein an optimum startup time and high rotation accuracy can be easily obtained at low cost under the conditions of low power consumption and downsizing.